This invention relates generally to spacers and, more particularly, has reference to a spacer which is capable of producing a force and taking up a tolerance to hold elements in place in an assembly. The invention is particularly suited for adaptation to an optical assembly where it can be used to hold optical elements, such as lenses, in place within a housing.
A common need which arises in numerous types of mechanical and other assemblies or structures is to hold elements or components in desired locations within the assembly or structure without permanently affixing them thereto or integrating them therewith. Various mechanical retaining devices have been designed to perform this function.
One particular type of assembly of interest is the optical assembly, known as the relay lens, which is found in a head-up display. As described in detail in U.S. Pat. No. 3,940,204, a head-up display is an optical display system, typically found in the cockpit of military fighter aircraft, which enables a pilot to see an artificially generated display of information superimposed on his view of the outside world. The relay lens consists of a housing assembly, generally in the form of a, hollow, cylindrical, barrel-like structure, which contains a longitudinal or axial stack of optical lenses arranged in predetermined sequence and relative orientation so as to define a light path through the housing assembly. In order for the relay lens to perform its intended optical function, the individual lens elements must be held in specified positions and orientations within the housing. Mechanical lens spacers have been used to perform that function. The lens elements generally cannot be permanently affixed to or integrated with the housing assembly without adversely affecting their optical properties.
The spacers used in head-up displays must be capable of developing sufficiently high load to hold the lens elements in place under the severe forces and vibrations often encountered in military fighter aircraft. Moreover, they must be capable of holding the lenses in place to the close tolerances needed to assure correct optical performance of the display system. In addition, the spacers must be designed to minimize weight which is always an important factor for fighter aircraft.
Spacers capable of producing a force and taking up a tolerance are known. However, these known spacers operate on the spring principle, i.e., they are designed to be compressed or deflected to develop the force or load needed to hold elements in place. A known spacer of this type specifically designed for use in a head-up display system is shown and described in detail below.
Known spacers operating on the spring principle suffer numerous deficiencies. Because they are designed to be compressed or deflected, they generally have relatively complex structures which are heavy, costly and difficult to manufacture. Their inherent compressibility makes them susceptible to loss of tolerance. In addition, they have often been found incapable of producing sufficient load to hold elements in place under all operating conditions.
Hence, a need exists for a new type of spacer which is lighter, less expensive and easier to manufacture than spring-type spacers and which is capable of producing high loads with little or no compression or deflection.